Three American crew members died Thursday when a C-130 Hercules aerial water tanker crashed while battling wildfires in southeastern Australia, officials said.

The cause of the crash was not immediately known, but New South Wales Rural Fire Service commissioner, Shane Fitzsimmons had said earlier in the day that high winds were making flying the water tankers “very difficult”.

“We’ve got a number of firefighters and a number of crew that are in the area who are working to contain and work around the fire,” Fitzimmons said.

The highly experienced US firefighting trio were working for Canadian firm, Coulson Aviation, which had been contracted to help fight the fires.

The tragedy brings the death toll from the blazes to at least 31 since September. The fires have also destroyed more than 2,600 homes and razed more than 10.4 million hectares (25.7 million acres) of land.